Wind energy installations are suitable as local generators of electrical energy, particularly also for use in thinly populated areas with favorable wind conditions. Many of these thinly populated areas are in zones with an adverse climate. These also include areas with a cold climate, in particular. In order to toughen up wind energy installations for operation under “cold climate” conditions, blade heating is usually necessary for the rotor blades. This is because it has been found that, without such heating, ice forms or collects on the rotor blades during operation, said ice having disadvantageous effects in multiple respects. Firstly, it alters the aerodynamic profile of the rotor blades, which usually results in significant impairment precisely when the rotor blades have a very advanced aerodynamic design. Furthermore, the formation of ice increases the weight of the rotor blade, which increases the forces to be absorbed by the suspension of the rotor blades; this applies particularly during operation at relatively high speeds and correspondingly growing centrifugal forces or when there are imbalances in the hub as a whole which are caused by different ice formation on the respective rotor blades. Finally, there is also a not inconsiderable risk to persons and objects in the vicinity of the wind energy installation as a result of ice being cast, i.e. as a result of pieces of ice becoming detached from rotor blades and being flung away. In general, the wind energy installation is shut down when there is ice formation on the rotor blades. In order to avoid these disadvantages, blade heating may be provided. On account of the size of the rotor blades and sometimes harsh climatic conditions, however, a relatively large amount of heating power is required for the blade heating. Providing said heating at the location at which it is needed, namely in the hub of the rotor, requires some additional complexity, resulting in additional cost.
In order to be able to still supply power to a large electrical load, such as a blade heater, without amplifying the power available in the hub, a design has become known in which the wind energy installation is shut down while the rotor blades are being heated (DE 103 23 785 A1). Although this has the disadvantage that no further electrical power is generated by the wind energy installation during the phases in which the rotor blades are being heated, this has the advantage that barely any power needs to be expended for the individual requirements of the wind energy installation during the shutdown, and hence all of the electrical power available in the hub can be used for heating the rotor blades. Usually, heating takes place over a period of up to 15 minutes, and after that the wind energy installation is started up again. Although heating using a stopping device of this type has proven itself in principle, this still has the disadvantage that no electrical energy is generated during the heating time, that is to say that the yield is reduced.
This is made even worse by the fact that restarting afterwards is extremely time consuming, which further reduces the production of energy by the wind energy installation. Above all, however, a serious disadvantage is that the ice formation per se is not prevented and hence a risk to the surroundings cannot be ruled out.